Pliabilization, as the term is used herein, refers to the process of stretching a knitted or woven structure in one or more directions so that the structure's dimension in that direction(s) is increased. For such knitted or woven structures, the increased dimension may result in a decrease in material thickness and/or an increase in pore size.
There many applications where pliabilizing a knitted or woven structure is desirable or necessary. For example, materials made of polysaccharides (which include cellulose based materials such as rayon, cotton, oxidized cellulose, ORC, etc.) are subject to shrinkage during processing or exposure to moisture, which makes the material less flexible. Pliabilization is needed for such materials in order to render the material less stiff and thereby useful for its intended purpose or application. In the case of ORC fabric, a benefit of pliabilization is to open the pore structure of the material to enable a more efficient drying step.
It is important to assure that pliabilization is achieved uniformly and in all directions. If pliabilization is not uniform, sections of the material may need to be removed and discarded to assure that the remaining material has uniform properties in all directions. If not, product performance may be affected.
When considering tubular knitted or woven structures, it is known to pass the tubular “socks” over enlarged apparatus to radially expand or stretch the sock. In many known devices, however, the enlarged apparatus is mounted in such a manner that continuous feed over it is impossible. Rather, the length of the sock that can be passed over the mandrel is limited due to the physical interference of the mounting mechanism. Another known prior art system is shown in FIGS. 1a and 1b, which includes opposing rings 10 held in place between respective pairs of cone shaped pins 12. As shown in FIG. 1b, the sock 14 is stretched as it is fed over the rings. This system, however, does not stretch the material equally around the circumference of the sock, but rather results in non-uniform, primarily two dimensional stretching. At least some known devices have attempted to address the issue of achieving radial stretching and continuous feed for stretching tubular fabrics. These devices are set forth in U.S. Pat. No. 1,775,894 and GB Patent No. 282,896. These disclosed machines are large and cumbersome, and rely on a series of sets of rotating wheels e extending along a relatively long pathway, as shown in FIG. 5 of the '894 patent. The disclosed machine also is not likely to result in uniform stretching, as the fabric will stretch and un-stretch repeatedly both as it passes successively from one set of wheels to the next, and also as between the circumferential wheels of any given set. Further, the disclosed stretching apparatus requires a large and cumbersome mounting mechanism to maintain its position relative to the frame as the fabric is passed over it.
Another disadvantage of the prior art devices described above is that the wheels over which the fabric is drawn for stretching are mechanically driven to assist in passing the fabric over them, which also results in less uniform stretching as the speed and/or tension placed on the fabric fluctuates over the course of the process.
The present invention provides a new and improved apparatus for pliabilizing continuous tubular knitted or woven structures in a uniform manner.